Age-related alterations in vitamin A metabolism in the rat retina

Electroretinogram measures in a septuagenarian population

This study reports electroretinogram (ERG) data in a septuagenarian population. Fifty healthy adults without diabetes or dementia aged 70-79 years underwent standardised electrophysiological testing incorporating current ISCEV Standards as baseline assessment for the OPAL (Older People And n-3 Long-chain polyunsaturated fatty acids) study. These data were compared with those from 53 healthy adults aged 20-50 years. Amplitudes and peak times of the major components were assessed. There were no significant differences in amplitude or peak time between sexes or between eyes. ERG amplitudes were 25-40% smaller and peak-times were longer in the older compared with the younger age group. In all participants, the bright flash ERG b-wave amplitude had the highest variability; the bright flash ERG a-wave peak time had the lowest. ERGs in a septuagenarian age group show 25-40% lower amplitude than those of a 20 to 50-year-old group and are of longer peak time. With an increasingly ageing population involved in clinical trials, and the potential use of ERG in the assessment both of efficacy and safety in forthcoming therapeutic interventions, it is important that the effects of age are given adequate consideration.

Photoreceptor degeneration and dysfunction in aging and age-related maculopathy

The relative rate of rod and cone degeneration is a fundamental characteristic of any disorder affecting photoreceptors, including aging and age-related maculopathy (ARM). The human macula consists of a small cone-dominated fovea surrounded by a rod-dominated parafovea. In aging and early ARM, rods degenerate before cones, a decline in scotopic (rod-mediated) sensitivity is more prominent than a decline in photopic (cone-mediated) sensitivity, and the time course of dark adaptation of rods slows dramatically. The topography of rod dysfunction and loss in early ARM matches the location of pathology in the retinal pigment epithelium (RPE)/Bruch's membrane complex visible in the ocular fundus. Rod dysfunction and loss in aging and ARM may be due to retinoid deficiency at the level of the photoreceptors cause by impaired retinoid translocation across the RPE/Bruch's membrane complex, a hypothesis deserving of further investigation.

Potential role of retinal pigment epithelial lipofuscin accumulation in age-related macular degeneration

Age-related macular degeneration (AMD) is a leading cause of severe visual impairment in developed countries. The vision loss associated with AMD is the result of degenerative changes in the central region of the retina called the macula. Maintenance of normal structure and function of the macular retina, and of the remainder of the retina as well, is critically dependent on the supporting role of the adjacent retinal pigment epithelium (RPE). Impairment of normal RPE functions is known to result in retinal degeneration and loss of visual function. Thus, it has been hypothesized that the retinal degeneration that characterizes AMD is secondary to age-related deterioration in RPE support functions. Like many other postmitotic cell types, the RPE accumulates autofluorescent lysosomal storage bodies (lipofuscin) during senescence. In human eyes, lipofuscin comes to occupy a substantial fraction of the RPE cytoplasmic volume in the elderly. Does this lipofuscin accumulation contribute to the development of AMD? This question is a specific case of the broader question of whether lipofuscin accumulation in general is detrimental to cells. Unfortunately, definitive data do not exist to allow these questions to be answered. Although a correlation between RPE lipofuscin content and AMD has been reported, a cause-and-effect relationship between RPE lipofuscin accumulation and the development of this disease has not been established. It has been reported that a mutation in a gene encoding a photoreceptor-specific protein results in massive RPE lipofuscin accumulation and early-onset macular degeneration. However, again the accelerated RPE lipofuscin accumulation has not been shown to be the cause of the accompanying macular degeneration. The lack of a definitive link between RPE lipofuscin accumulation and AMD illustrates one of the biggest challenges remaining in lipofuscin research-determining whether lipofuscin accumulation per se has an impact on cell function.

Light and aging effects on vitamin E in the retina and retinal pigment epithelium

Experiments were performed to determine the effects of senescence and light adaptation on vitamin E levels in the neural retina and RPE-choroid-sclera of pigmented rats. Aging resulted in significant increases in alpha-tocopherol levels in both tissues, the effect being most pronounced in the RPE-choroid-sclera. The state of light adaptation had no influence on alpha-tocopherol levels in the neural retina at any of the ages examined, whereas in the RPE-choroid-sclera, alpha-tocopherol levels were substantially higher in light-adapted than in dark-adapted animals at all three ages (12, 22, and 32 months) at which they were measured. The effect of light adaptation on RPE-choroid-scleral alpha-tocopherol levels was most pronounced in the oldest age group.